Radio communication systems perform high-speed data transmission using MIMO (Multi Input Multi Output). Such systems include WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), and LTE-A (LTE Advanced), by 3GPP (Third Generation Partnership Project), and wireless LAN and WiMAX (Worldwide Interoperability for Microwave Access) by IEEE (The Institute of Electrical and Electronics engineers). The radio communication system includes a plurality of transmit and receive antennas in each of base stations (cells, transmit stations, transmitters, and eNodeB) and terminals (mobile terminals, receive stations, mobile stations, receivers, UE (User Equipment)).
The radio communication system measures channel state information between a base station and a terminal using channel-state information reference signal including known signals between the base station and the terminal (CSI-RS (Channel State Information-Reference signal), a pilot signal, and known signals)), and then adaptively controls modulation system and coding rate (MCS (Modulation and Coding Scheme)), spatial multiplexing numbers (number of layers, and rank), and precoding weight (a precoding matrix, and a precoder) in accordance with measurement results. The radio communication system thus performs data transmission more efficiently. For example, a method described in Non-patent Literature 1 may be used.
FIG. 20 schematically illustrates an example of adaptive control that is performed to transmit data in a downlink in a single-cell communication. As illustrated in FIG. 20, a base station 2001 transmits to a terminal 2002 (configures the terminal 2002 with) a channel state information-reference signal via a downlink (downlink line) 2003. A terminal 2002 measures channel state of the downlink 2003 in accordance with the received channel state information-reference signal of the base station 2001. The terminal 2002 transmits (feeds back) to the base station 2001 information for adaptive control (feedback information and report) via an uplink (uplink line) 2004.
The radio communication system may be arranged in a cellular structure in which a coverage area of the base station includes a plurality of cells, and a communication area is thus expanded. With frequencies different depending on adjacent cells (sectors), a terminal in a cell edge portion of the cell can communicate without interference, but a problem of frequency use efficiency still remains. For this reason, repeated use of the same frequency in each cell (sector) dramatically increases the frequency use efficiency, but a remedial step to interference on a terminal in the cell edge (cell end) area becomes necessary.
Under these circumstances, methods have been studied to reduce or suppress interference on the terminal at the cell edge area using an inter-cell cooperative communication as a multi-cell communication (cooperative communication). In the cell cooperative communication, adjacent cells cooperate with each other. For example, CoMP (Cooperative Multipoint) transmission scheme has been studied as described in Non Patent Literature 2.